Pulse generator



Feb. 12, 1952 J. R. WILKERSON PULSE GENERATOR Original Filed June 14, 1944 U. Q ww wg 6 FYI a 5 6 l o W W L L I f rH m a ma N 5 Dc me pc H f WMM mm a UHE @j UR OWG ,P0 0 5 F 6 R :J/ E*R W/ E+@ E n? m www mf TW 5 aCPeHv wlw S @7Min/ l EE ED Ts Dw 0 5 I N V EN TOR. d. f?. l/l//LKE/Pso/v Patented Feb. 12, 1952 PULSE GENERATOR Jefferson R. Wilkerson, Hempstead, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Original application' June 14, 1944, Serial No.

1948, Serial No. 41,116

Claims.

My invention' relates to circuits for electric discharge devices such as vacuum tubes, and concerns particularly pulse. forming circuits and synchronizers.

This invention is a divisionof my prior application Serial No. 540,322, led. on June 14, 1944, nowPatent No. 2,520,989, dated September 5, 1950.

It is an object of the present invention to provide an improved non-linear'or peaking coil generator which is' free from .phase shift. This type of coil, sometimes known as a Peterson coil, normallyincludes a core consisting of a ferromagnetic material of high permeability at low iield strength such as Permalloy which saturates with minute exciting currents. This type of coil is also sometimes known as a saturable reactor.

An object ofthe present invention is to provide an improved pulse former and synchronizer for radio object detecting systems.

Another object of the present invention is to provide arrangements .for making accurate range measurements.

Still another object is to insure that the phase of the output pulse of a. pulsegenerator is uneffected by changes in vacuum tube characteristics, variation in input voltage, or'variations in voltage supply.

A still further object is to provide a vacuum tube circuit having a, non-sinusoidal output with delayed automatic control and negative feedback supplied by a common connection.

Still another object of the present invention is to avoid-variation in amplitude of the sine wave voltage applied to the non-linear or Peterson coil of a pulse generator.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in connection with range indicating object detecting systems of the microwave type, I provide a synchronizer including two pulse-generating circuits each responsive-tesine wavevoltage: Oneofthe pulsegenerating circuitsV is utilized as a transmitter trigger for releasingv microwave pulses in accurately fixed phase'relationship with respect to an input sine'wa-ve. The other pulse-former'circuit is utilized for producing indicator timereference pulses for range indication accurately set in phase. Range is indicated by-comparison lof the position of thek reference 'pulse-with a video-*signal received as ai result of' reflection of the transmitted wave in the event that an object is detected by intercepting the'transmittedl wave.

In carryingl out the. invention inits preferred Divided and this application July 28,

(Cl. Z50-27) form, each pulse generator circuit comprises a voltage ampliiiei` and a power ampliiier in cascade with a tuned series resonant circuit coupled to the output of the power amplifier and supplying current to a saturable core inductance of the non-linear or Peterson coil type for producing sharp peaked waves or pips in synchronism with the sine wave input. Preferably, the circuit constants are so chosen that the amplifiers operate as class A amplifiers. I provide a negative feedback stabilizing connection from the tuned circuit to the input vof the power amplifier and I provide a delayed automatic volume control for the voltage amplifier energized by the same feedback connection.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing, in which I Fig. 1 is a circuit diagram of a pulse generator forming an embodiment of my invention;

Fig. 2 is a schematic diagram of an objectdetectingand range-indicating system, embodying my invention;

Fig. 3 is a graph illustrating the principle of operation of the pulse-generating circuit illustrated in Fig. l;

Fig, 4 is a diagram of the indicator screenwith a graph explanatory of the principle of operation, and

Fig. 5 is a graph explaining the manner of obtaining a Vernier eiect.

Like reference characters are utilized throughout the drawing to designate like parts.

The circuit illustrated in Fig. 1 comprises a first stage amplifier II which may be a voltage amplifier, asecond stage amplier I2 which may be a power amplier, a series-resonant tuned circuit I3 energized by the ampliiier I2, a saturablecore reactor I4 in series with the tuned circuit I3, and means for obtaining an output voltage from the saturable-core reactor IG. An input terminal I5 isv provided which is adapted to be connected to a source of sine-wave signal-frequency voltage represented schematically as a generator I6. The generator IB may be a radicfrequency generator, but my invention is not limted to vuse with radio-frequency apparatus. An output terminal I'l is provided which is coupled to the saturable-core reactor I4 by a coupling condenser I 8 and a load resistor I9.

For supplying delayed automatic volume control, a diode detector may be provided and for convenience the diode detector and the voltage or iirst stage amplifier may be combined in a 3 single evacuated envelope 2| o1 a duplex tube, such as a diode-pentode tube of the 6SF7 type, for example. The envelope 2l contains a conventional cathode 22, shown as grounded, a conventional anode 23, an input signal grid 24 and conventional suppressor and screen grids, all of which form a pentode voltage amplifier. In addition, the envelope 2| contains a diode-anode Y 25, which, together with the cathode 22, forms an automatic volume control diode detector. Thus a single cathode serves both the pentode amplifier and the automaticevolume-control diode detector.

The power amplifier stage I2 may take the form of a beam power amplifier tube comprising the conventional electrodes including an input grid 26, resistance-capacitance coupled to the anode 23 of the voltage amplier I I, and an anode Y 21 coupled to the tuned circuit I3. As shown, a coupling transformer 28 is provided for cou.- pling the anode circuit oi' the power amplier I2 to the tuned circuit I 3.

The tuned circuit I3 includes a condenser 29 and an inductance coil 3l connected in series and having such constants as to be resonant at substantially the frequency of the input sine wave source I6, which may, for example, supply a voltage at 100 kilocycles per second.

The saturable-core reactor I4 connected in series with the tuned circuit I3 may be of the type having a core composed of a material such as Permalloy designed to saturate with minute exciting current and which may be constructed as described by Peterson, Manley and Wrathall in their article Magnetic Generation of a Group of Harmonics, published in volume 16 of the Bell System Technical Journal for October 1937, pages 437 to 455, and also published in Electrical Engineering, August 1937.

For Vsupplying anode current to the vacuum tube stages I I and I2, aconventional source of unidirectional voltage is provided, here represented for convenience as a battery of cells 32, With a negative terminal grounded and a positive terminal by-passed by a condenser 33 to eliminate the signal-frequency impedance of the voltage source 32.

The common terminal 34 of the series resonant condenser 29 and inductance coil 3! is coupled by means of a conductor 35 and a condenser 39 to the input signal grid 26 of the power amplifier I2. The connections of the transformer 28 are such that the coupling circuit 36, 35 supplies negative feedback or degeneration to the power amplifier I2.

For supplying the automatic volume control diode 25, 22, the conductor 35 is also coupled to the diode-anode 25 by means of a condenser 31. For setting the level above which the automatic volume control comes into effect and providing voltage delayfk the input signal grid 24 and the diode-anode Y25 are positively biased by means of a pair of resistors 38 and 39 connected in series between the positive terminal of the power supply 32 and the diode-anode 25, the common terminal 4I of the series resistors 38 and 39v being connected to the signal input grid 24. Preferably the resistance of the resistor 39 is made less than that of the resistor 38.

The manner in which the sine wave input Voltage is converted into sharp peaks of the Wave form illustrated at 42 may be explained briefly as follows;

Since the stages I I and I2 are operated as lclass A amplifiers, the sine wave voltage provided by the generator I6 will be applied with increased amplitude and pure sine wave to the tuned circuit I3 which, being resonant, will cause a substantially pure sine wave current to pass through the saturable-core reactor I4. Owing to the high degree of saturationof the core, however, the reactance thereof will vary greatly between the maximum value with small input current and a greatly reduced value with somewhat larger input currents. As a result, there is a switching eiect and sharp voltage peaks 42 are produced at the vcross-over points of the input sine wave 43, illustrated in Fig. 3. The principle of operation of this part of the circuit is described in greater detail in the aforesaid article in the Bell System Technical Journal.

Nevertheless, the precise phase relationship between the output pulse and the input sine wave depends, I have found,l upon the magnitude of the sine `wave current supplied to the saturable core reactor I4. 'I'he phase angle depends 'also upon the magnitude of the voltage supplied by the source 32 and 'is subject to variation with variations in tube characteristics causedv by aging, variations in ambient temperature, etc. Some phase shift between .the input and output waves is not objectionable, but any such phase shift must be held constant in order to obtain accuracy, precision and reliability in a ranging system.

The negative feedback through the coupling condenser 36 lstabilizes the power amplier and overcomes phase angle variation from variation Y in supply voltage and tube characteristics. The delayed automatic-volume control provides for maintaining substantially constant the effective value of the sine wave current in the saturablecore reactor I4.

The manner in which delayed automatic volume control is obtained results from the novel connections employed. The resistors 38 and 39 in series form a voltage divider for supplying a predetermined D. C. level voltage to the grid 24. Furthermore, these resistors connect the diodeanode 25 to the positive terminal of the voltage supply 32. In the absence of automatic-volumecontrol voltage the grid 24 will draw slight grid current so that the grid is slightly positive. The tube II will then operate as an amplifier with approximately maximum gain. If it is assumed that the ratio of resistors 38 and 39 is 2.5:1 and the voltage of the source 32 is 250 volts, the grid 24 will continue to draw current until the rectied control voltage on the diode-anode 25 exceeds approximately volts. At this point the grid 24 ceases to draw current and is drawn negative at about three-quarters of the rate at which the control voltage increases. This in turn reduces the gain of the amplifier II and so furnishes a very eiective delayed automatic volume control.

A highly precise object locating and rangemeasuring system utilizing pulse-forming circuits such as illustrated in Fig. l is shown inI Fig. 2. The arrangement of Fig. 2 is a modification of the arrangement disclosed in the application of Joseph J. Caldwell, Jr.,'and Robert F. Hays, Jr., Serial No. 443,573, yiiled May 19, 1942. It will be understood that those parts of the system not essential to the understanding of the function of the pulse-forming circuits are either omitted or indicated only schematically.

The system of-Fig. 2 comprises a pulse transmitter 44, a pulse receiver-45, a cathode raytube 46, utilized as anv indicator, an accurately maintained source of radio frequencysuch as a 100 kilocycle crystal oscillator represented by the sine tripping the pulse `former 48 for convertingthe output sine wave of casamos wave source 16, a transmitter trigger lcircuit f4.1 *for-converting the output of 'thesine --wavegenerator l6'into Vaccurately phasedV trigger pulses for transmitter `44, and a pulse the generator I6 into` accurately 4phased-pulses or pips to serve as range reference indications in the cathode ray tube46.

The units 41 and 48 are pulse generatorssuch as shown in Fig. 1.

`A single antenna may be employed for the 'transmitter 44 andthe receiver:45, butfor the sake of simplifying the drawingseparateparaboloid type antennaeA-,49-arershown.

The` cathode ray tube 46, which is shownfrag- -mentarily, comprises the 4conventional.elements including a control grid 52,.connected to4 thevideo output ,terminal of the pulse receiver 45, a timesweep circuit including a .sweep-,generatort and deflection plates 5l, and a transverse sweep cir- -cuit shown as comprising sweep plates 53, adapted to be coupled to the puls-e former 48.

In order to provide for very precise indications of range the period of the transverse sweep wave applied to the sweep plates 53 may be made a small fraction of the maximum range of the system, in which case a sub-multiple transverse sweep wave is also required. As illustrated in Fig. 2, a frequency divider 54 may be provided which receives its input signal from the output of the sine wave generator I6. A square-wave generator 60 is interposed in the output of the frequency divider 54. For combining the outputs of the sub-multiple frequency square-wave generator 60 and the pulse former 48, an addition circuit 55 may be provided; and a biased cathodefollower circuit 56 or clipper may also be provided for preventing the outp t of the addition circuit 55 from reaching the sweep circuit including the plates 53 except when the output of the addition circuit exceeds the value of the peak voltage output of one of the devices 48 and 54.

Corresponding elements 66a, 55a and 55a are provided for causing the transmitter 44 to be trisgered at the sub-multiple frequency at which the range indicator plates 53 are energized.

Although the horizontal scale of the screen of the tube 46, shown in Fig. 4, may be calibrated in terms of range, the range scale may be made independent of the degree of linearity of the circuits by means of a null system utilizing phase shifters 51 and 58 for adjusting the position of the reference pulse on the screen of the cathode ray tube 46 to coincide with the position of a video signal 59 produced by the pulse receiver 45 when the target is detected.

If it is assumed that the frequency divider 54 has a ratio of to 1, a mechanical connection 6|, such as a 20:1 reduction gear represented by a dotted line, may be provided between the control or adjusting arms 62 and 63 of the phase Shifters 51 and 58 so that the latter serves as a coarse phase shifter. Y

The grid 52 of the cathode ray tube 46 is so biased that normally the tube 46 is reduced in intensity and it produces only a faint trace, but no bright indication or spot on the screen of the tube. However, when a video signal is received by the receiver 45 the grid 52 is energized more strongly and the bright spot 55 is produced upon the screen. If the `clipper 56 were not employed, the cathode ray beam 64 would be swept along the screen transversely by the sweep circuit 53 so as to produce a trace corresponding to the sum ofthe peak .output wave 4210i thepulseformer 48 .and Ethe squareoutput wave 65.01 :the squarewave generators 6 6 and66a. ('Fig.5) A

The bias fof the .cathode :follower clipper;56 causes all of the Wave of'Fig.;5 tosbeeliminated except Vthe marker 42 `which=produces suchaitrace on the screen of the cathode ray tube i46. The maximum rangev of the system is such :that only one ofthe square pulses 65'su-pplied by fthe-circuit 54 occurs during Vthe timecorrespondingvto maximum range. However, forthe constants'iassumed 20 sharp pips `'42.occur during .thefsame time period. Only zone Aof these v-pulses 1.42 appears upon the screen of-fIFig.-4, namely,theone corresponding to the time period during .which thesquare-wave65 is appliedlto the screen circuit. *For accuracy and-precisionfof--range indication, the phase-angle ofthe-pip-42 `musteremain lconstant-for a givenf-phase'shif-ter setting regardless of any variations in strength 'of-input signal, voltage 'supply or tube characteristics. The constant phase-angle pulse-generators 41 and 48 are therefore very important to the proper operation of the range-indicating system. Since the position of the square-wave 65 is determined by the setting of the coarse phase shifter 58 and the positions of the sharp pips 42 with respect to the square-waves 65 are determined with great precision and reliability by the setting of the phase shifter 51, the phase Shifters may be so set as to cause the single reference pip 42 which appears upon the screen of Fig. 4 to intersect the video target 59 and the range may be read from the settings of the control arms 62 and 63 of the phase shifters 51 and 58 respectively.

It will be understood that the phase shifter-s 51 and 58 may be calibrated in phase angle, time duration, or preferably directly in range.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A pulse generator comprising in combination, a voltage amplifier having an input terminal to which a sine wave source may be connected, a power amplifier with an input coupled to the voltage amplifier, a tuned circuit coupled to the output circuit of the power amplifier, a non-linear coil connected to said tuned circuit, an output terminal coupled to said non-linear coil at which the peak wave output may be obtained, a negative feedback coupling between said tuned circuit and the input to the power amplifier, and an autom-atic volume control device coupled to said tuned circuit and to the input of said voltage amplier.

2. A pulse generator comprising in combination, a voltage amplifier having an input terminal to which a sine wave source may be connected, a power amplifier with an input coupled to the voltage amplifier, a tuned circuit coupled to the output circuit of the power amplifier, a saturablecore reactor coil connected to said tuned circuit, an output terminal coupled to said saturable-core reactor coil at which the peak wave output may be obtained, and an automatic volume control device coupled between said tuned circuit and the input to said voltage amplifier. l

3. A pulse generator comprising in combination, a voltage ampliiier having an input terminal to which a sine wave source may be connected, a

power amplifier with an input coupled to the volta-ge amplier, a tuned circuit coupled to the output circuit of the power amplier, a nonlinear coil connected to said tuned circuit, an output terminal coupled to said non-linear coil at which the peak wave output may be obtained, and an automatic volume control detector with an input connection interposed between the amplifying means and the output circuit, a bias connection supplied by said automatic volume control detector and a coupling between said bias connection on the input side of the amplier.

4. Apparatus as in claim 3 including a positive bias for delaying the automatic volume control eiect.

5. A pulse generator comprising in combination, iirst and second stage amplifying tubes, a diode detector associated with the rst amplifying tube, coupling between the rst and second amplifying tubes, a tuned circuit and a saturab1e core reactor in said tuned circuit, said second stage amplifier having an output connection to the tuned circuit and an input connection with a degenerative coupling from the tuned circuit to the input connection of the second stage amplier, said rst stage amplier having an input connection energized by the diode and a positive bias for said input connection, and the diode being coupled to the tuned circuit.

JEFFERSON R. WILKERSON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

